OS X Yosemite: Set up users on your Mac
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guest user: Guest users can use your computer temporarily without you having to add them as individual users. You can set restrictions guests can access only the items you want to share. Files created by a guest are stored in a temporary folder, but this folder and its contents are deleted when the guest logs out. The guest account works with the Find My Mac feature of iCloud, which can help you find your Mac if you lose it. You can locate your Mac if someone finds it, logs in as a guest, then uses Safari to access the Internet.
Guests:
Don’t need a password to log in
Can’t change user or computer settings
Can’t log in remotely when remote login is turned on in Sharing preferences
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Seems like a secure setup, in theory.
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